1. Field of the Invention
The present invention relates generally to the field of propulsion systems for watercraft, such as pleasure craft, fishing boats, pontoon boats, ski boats, and so forth. More particularly, the invention relates to a technique for trimming a propulsion system which includes a pair of electric motor-driven props operated in coordination to provide a desired resultant thrust.
2. Description of the Related Art
Various propulsion systems have been proposed and are currently in use for watercraft, such as pleasure craft and fishing boats. Such propulsion systems may typically be classified as either internal engine-based systems, or electric motor-based systems. In the first class, an internal combustion engine is operatively connected to a prop to produce a thrust used to propel the boat through the water. Systems of this type include conventional outboard motors, inboard motors, and the like.
Electric drives, commonly referred to as trolling motors or electric outboards, typically include an electric motor which is energized to rotate at various speeds to drive a prop. In a conventional configuration, the electric motor and prop are provided in a propulsion unit which is submerged when the motor is deployed. Directional orientation of the propulsion unit, through a manually or remotely positionable support tube, determines the direct of the resultant trust and thereby the direction of navigation of the boat.
While propulsion systems of the foregoing types are suitable for many applications, they are not without drawbacks. By way of example, internal combustion engines are simply inappropriate for certain activities, such as fishing, due to their noise and thrust levels. Trolling motors and electric outboards offer quiet and controllable navigational devices, but also have fairly limited controllability, particularly directionally due to the need to rotate the devices during use. The conventional trolling motors are also subject to damage upon contact with submerged objects, and may become entangled in weeds and plant growth as the boat is displaced in shallow waters.
A novel propulsion system has been proposed that includes a pair of propulsion units spaced from one another and secured to a boat hull. The propulsion units each include a variable speed electric motor and a prop rotated by the motor during operation. By coordinating the rotational speeds of the motors, components of a desired resultant thrust may be generated by the units to navigate the boat in various directions. The system offers considerable advantages over heretofore known propulsion systems, including inherent controllability, lower maintenance and deployment times, inherent protection from submerged objects, and so forth.
A challenge in the control of the new propulsion system resides in the appropriate coordination of the rotational speeds of the motors, both over forward and reverse speed ranges. There is a need, therefore, for a technique designed to control such a system. There is a particular need for a technique which is both intuitive and relatively straightforward to implement.